Most electronic devices emit some electromagnetic inference radiation. For devices having a display, a significant amount of the interference passes through the display. In modern devices, the display is usually a liquid crystal type due to light weight, thinness, and low power consumption. Prior art methods have attempted to suppress electromagnetic interference radiation emission through the display by providing a suppression sheet or coating over the display. The suppression sheet or coating is typically formed of a substantially transparent electrically conductive material. The conductive material is electrically connected to the chassis or case for the electronic device, which suppresses or attenuates the emission of interference radiation through the display. As the suppression sheet or coating is substantially transparent, viewing of the display is largely unhindered.
While satisfactory for some purposes, there has been an increasing trend toward use of touch sensitive displays. The preferred technique for providing touch sensitive functionality has recently been to use capacitive sensing techniques. Capacitive sensing permits the sensing of multiple simultaneous touches for a wider range of inputs from a user. Unfortunately, using a conductive transparent conductive sheet or coating to suppress electromagnetic interference through the display tends to adversely impact capacitive sensing.
Regulations pertaining to aircraft generally impose the most stringent requirements for the level of electromagnetic interference that can be permissibly emitted by a device. There are two areas of the electromagnetic spectrum that tend to be problematic for electromagnetic emissions from electronic devices in aircraft. The first is the very high frequency range (VHF), reserved for pilot communication. The second is the frequency range reserved for the global positioning system (GPS).
The present invention addresses the problem of suppressing electromagnetic interference from an electronic device.